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Epidemiological data on Steinert desease - Different forms of myotonic dystrophy - Transmission of myotonic dystrophy - Signs of myotonic dystrophy 

Responsible genes - How is myotonic dystrophy diagnosed - Risks of myotonic dystrophy - Treatment of myotonic dystrophy

 
Type 1 Myotonic dystrophy or Steinert disease

    A characteristic of Myotonic Dystrophy is the wide variability of its expression. Certain individuals will be very affected by the disease while others will show very little signs of it. Certain individuals can also be carriers of the genetic anomaly but show no sign at all of the disease. This variability is seen within different families as well as within the same family. Generally, the overall severity of the disease can be predicted by the age at which it first manifests, of its clinical signs, and of its evolution. Earlier onset of the disease brings greater chances of being highly affected by it.

The median age for onset of the disease is 20 to 25 years of age but since there is great variability and since symptoms sometimes go unnoticed, the disease is often undiagnosed until later, when the patients are in their forties. In addition to the classic form of the disease (above), there are early forms of the disease (juvenille) and the disease can manifest at birth (congenital form).

The following presentation will describe the principal signs/symptoms of the disease.

 

    Muscle weakness: Muscle weakness mainly affects the head and neck and then moves to the extremities.  This weakness is responsible for mastication problems. When this weakness is severe it causes a slack jaw and open mouth. Usually face muscle weakness will cause droopy eyelids. Weakness of the palate, tongue and vocal cords is responsible for a change in voice quality that then becomes nasal. Weakness of the muscles of the pharynx can bring on dysphagia (difficulty swallowing) to different degrees. Atrophy and weakness of neck muscles is frequent. This weakness causes difficulty with lifting the head from the pillow and can ultimately cause an anterior flexing of the head (bent toward the back).

When chest muscles are affected, respiratory amplitude can be reduced which may bring on chronic respiratory failure. Weak abdominal muscles will cause a slight pouch.

The muscles of the extremities are the most affected. Weakness and atrophy affects the lower leg muscles and causes droopy feet. Regarding the arms, weakness mostly affects the forearms and hands and in particular the fingers and wrists.

During the evolution of the disease muscle weakness can extend to the shoulders and pelvic girdle.

    Myotonia: It is a lack of muscle release after a sustained contraction. It is painless, stimulated by the cold, by fatigue and reduced by heat and repetitive movements. It disappears during sleep. Subjects often describe the phenomenon by saying: “My hands lock up”. Myotonia can be clearly seen by asking the subject to squeeze his/her hand and then rapidly release. Subjects with the disease are unable to open their hand quickly. The phenomenon can also be provoked by tapping the muscle sharply, known as percussion.
Ocular manifestations:

The principal ocular manifestations that are observed in this disease are cataracts that are present in nearly 100% of patients and can sometimes be the only sign of the disease. Other ocular manifestations such as diplopia (double vision), intra-ocular hypotension and keratites are non specific to the disease.

    Cardiac manifestations : Trouble with cardiac rhythm and conduction will arise first and can cause shortness of breath, discomfort, palpitations, syncope (brief loss of consciousness) and in severe cases, sudden death. Certain studies rate the risk of sudden death at 10%.
    Other manifestations of the disease: A certain degree of baldness is frequently observed in the men affected by the disease. Baldness is otherwise very rare in women. From an endocrine perspective, men affected by the disease often suffer from testicular atrophy that does not result in infertility. Hypersensitivity to insulin resulting from a peripheral resistance to insulin is present, but no diabetes is linked to the disease. Reduced hearing is frequently observed but often overlooked. It can be verified by audiometric tests. Regarding digestion, signs are inconsistent and range from difficulty with swallowing to constipation. Biliar lithiasis (gallstones) can be observed and will cause about a third of the patients to undergo a cholecystectomy.

Regarding behaviour, the disease can cause a reduction in activities (hypoactive individual) and sometimes the presence of great fatigue/drowsiness is present and can be very detrimental to professional life. There is sometimes a manifestation of sleep apnoea but it does not seem to be the cause of the great fatigue/drowsiness that is present in the majority of subjects.

    Myotonic Dystrophy and pregnancy : Pregnancy and delivery can present certain dangers for women affected by this disease. The principal complications observed during pregnancy are a high rate of miscarriages, premature births and complications at delivery. Infant mortality is also elevated and estimated at 160/1000 births compared to 19/1000 births within the population not suffering from the disease.

One of the great risks of pregnancy for a woman suffering from Myotonic Dystrophy is the chance of giving birth to a child with the congenital form of the disease. This can manifest in a severe form including congenital malformations and significant respiratory distress that can cause the death of the infant within the first days or months of life. The congenital form of the disease can sometimes be less severe in which case the infant will be hypotonic (floppy baby), have trouble swallowing and evolving into slow muscle development and severe mental retardation. The congenital form is only seen when the woman is affected by the disease. Some rare cases have been reported in cases where the father was affected by the disease but they remain exceptional.

Type 2 Myotonic dystrophy

    In 1994, a particular form of Myotonic Dystrophy with a different genetic anomaly than classic Myotonic Dystrophy (DM1) was described. Since the proximal (near) muscles were mainly affected by this form of the disease it was first called Proximal Myotonic Myopathy (PROMM) and then Type 2 Myotonic Dystrophy because of its similarities to Steinert Disease.

 
    Muscle weakness and atrophy: Muscle weakness affects face and neck muscles but is much less severe than in DM1. Regarding limbs, muscle weakness mostly affects the hips and shoulders. Moderate weakness in the feet and hands can happen as the disease evolves but is rarely an early symptom. Muscular atrophy is moderate in this form of Myotonic Dystrophy. In fact, hypertrophy of the calf muscles (elongation) is often observed in this form of the disease.
    Myotonia : Myotonia is often described by affected subjects as the locking up of hands. It is moderate and not very debilitating. Myotonia is much more variable over time than in the DM1 form.
    Pain: Muscle pain is frequent but unrelated to the severity of the myotonia or with exercise.
    Ocular manifestations: Cataracts develop before the age of 50 and have the same characteristics as those associated with DM1.
    Cardiac manifestations : Cardiac problems are far less frequent than in DM1. They are limited to First-Degree atrioventricular blocks or branch blocks. Cardiac complications are generally less severe although some cases of sudden death have been reported. Pacemaker implants and severe arrhythmia have also been reported. Contrary to DM1, there is no manifestation of respiratory failure.
    Cerebral manifestations : The disease’s effect on executive function is similar to that observed in DM1 although much less severe. Personality changes can be observed as well as poor performance concerning certain functions. There is no mental retardation linked to this form of Myotonic Dystrophy as there is in the congenital and early forms of DM1.
    Endocrine manifestations: Testicular atrophy is sometimes present in men as well as a peripheral resistance to insulin but these manifestations are less severe than in MD1. There is no available data linking thyroid disease and DM2. Pregnancy is an aggravating factor for pain, myotonia and muscle cramps. Affected subjects often complain of sweaty palms.
Type 3 Myotonic dystrophy

    In 2004, a particular form of Type 2 Myotonic Dystrophy linked to dementia was reported in a French family but that had nothing to do with the mutation responsible for DM2. A genetic link was found on chromosome 15. This rare form was called: Type 3 Myotonic Dystrophy (DM3).

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